U.S. Pat. No. 5,279,639, of Frank L. Kemeny et al., discloses a composition for synthesizing and treating ladle slags comprised of from about 5 to about 50 percent of calcium carbide, from about 10 to about 20 weight percent of magnesium carbonate, from about 40 to about 55 percent of calcium carbonate, from about 5 to about 20 weight percent of alumina, and from about 2 to about 5 weight percent of coke. The entire disclosure of this United States patent is hereby incorporated by reference into this specification.
The composition of such Kemeny patent is effective and has achieved a substantial amount of commercial success. However, since the commercial introduction of this composition, pressures have increased upon the steel making industry to substantially increase productivity, especially with the increased sales of foreign steel dumped into this country. One problem with the prior Kemeny composition is that is takes a relatively long period of time for it to treat the slag in order to produce the desired slag composition.
The desired refining slag composition disposed on top of the steel in the ladle will vary according to steel grade and other parameters. In general, however, this desired refining slag composition is comprised of from about 45 to about 65 weight percent of calcium oxide, from about 5 to about 30 weight percent of aluminum oxide, from about 5 to about 15 weight percent of magnesium oxide, from about 4 to about 25 weight percent of silicon oxide, from about 0 to about 15 weight percent of calcium fluoride, and from about 0.1 to about 8 weight percent of a mixture containing ferrous oxide and manganese oxide.
The desired refining slag preferably serves to provide a continuous partially molten oxide phase on the surface of the steel being treated, to capture and retain inclusive non-metallic material present in the steel (such as aluminum oxide), to be either non-oxidizing or reducing with respect to the steel, to control the sulfur content of the steel, to provide a non-corrosive environment for the refractory ladle linings, to promote stable arcing during electric arc reheating in the ladle, to protect the steel from contact with the atmosphere, and to provide thermal insulation.
It is an object of this invention to provide a novel additive for treating ladle slag which more readily facilitates the production of the desired ladle slag than prior art compositons.
It is another object of this invention to provide a novel additive for treating ladle slag which achieves the desired results at a lower concentration than prior art compositions.